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Subject[PATCH AUTOSEL 5.5 14/28] arm64: smp: fix smp_send_stop() behaviour
Date
From: Cristian Marussi <cristian.marussi@arm.com>

[ Upstream commit d0bab0c39e32d39a8c5cddca72e5b4a3059fe050 ]

On a system with only one CPU online, when another one CPU panics while
starting-up, smp_send_stop() will fail to send any STOP message to the
other already online core, resulting in a system still responsive and
alive at the end of the panic procedure.

[ 186.700083] CPU3: shutdown
[ 187.075462] CPU2: shutdown
[ 187.162869] CPU1: shutdown
[ 188.689998] ------------[ cut here ]------------
[ 188.691645] kernel BUG at arch/arm64/kernel/cpufeature.c:886!
[ 188.692079] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[ 188.692444] Modules linked in:
[ 188.693031] CPU: 3 PID: 0 Comm: swapper/3 Not tainted 5.6.0-rc4-00001-g338d25c35a98 #104
[ 188.693175] Hardware name: Foundation-v8A (DT)
[ 188.693492] pstate: 200001c5 (nzCv dAIF -PAN -UAO)
[ 188.694183] pc : has_cpuid_feature+0xf0/0x348
[ 188.694311] lr : verify_local_elf_hwcaps+0x84/0xe8
[ 188.694410] sp : ffff800011b1bf60
[ 188.694536] x29: ffff800011b1bf60 x28: 0000000000000000
[ 188.694707] x27: 0000000000000000 x26: 0000000000000000
[ 188.694801] x25: 0000000000000000 x24: ffff80001189a25c
[ 188.694905] x23: 0000000000000000 x22: 0000000000000000
[ 188.694996] x21: ffff8000114aa018 x20: ffff800011156a38
[ 188.695089] x19: ffff800010c944a0 x18: 0000000000000004
[ 188.695187] x17: 0000000000000000 x16: 0000000000000000
[ 188.695280] x15: 0000249dbde5431e x14: 0262cbe497efa1fa
[ 188.695371] x13: 0000000000000002 x12: 0000000000002592
[ 188.695472] x11: 0000000000000080 x10: 00400032b5503510
[ 188.695572] x9 : 0000000000000000 x8 : ffff800010c80204
[ 188.695659] x7 : 00000000410fd0f0 x6 : 0000000000000001
[ 188.695750] x5 : 00000000410fd0f0 x4 : 0000000000000000
[ 188.695836] x3 : 0000000000000000 x2 : ffff8000100939d8
[ 188.695919] x1 : 0000000000180420 x0 : 0000000000180480
[ 188.696253] Call trace:
[ 188.696410] has_cpuid_feature+0xf0/0x348
[ 188.696504] verify_local_elf_hwcaps+0x84/0xe8
[ 188.696591] check_local_cpu_capabilities+0x44/0x128
[ 188.696666] secondary_start_kernel+0xf4/0x188
[ 188.697150] Code: 52805001 72a00301 6b01001f 54000ec0 (d4210000)
[ 188.698639] ---[ end trace 3f12ca47652f7b72 ]---
[ 188.699160] Kernel panic - not syncing: Attempted to kill the idle task!
[ 188.699546] Kernel Offset: disabled
[ 188.699828] CPU features: 0x00004,20c02008
[ 188.700012] Memory Limit: none
[ 188.700538] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---

[root@arch ~]# echo Helo
Helo
[root@arch ~]# cat /proc/cpuinfo | grep proce
processor : 0

Make smp_send_stop() account also for the online status of the calling CPU
while evaluating how many CPUs are effectively online: this way, the right
number of STOPs is sent, so enforcing a proper freeze of the system at the
end of panic even under the above conditions.

Fixes: 08e875c16a16c ("arm64: SMP support")
Reported-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm64/kernel/smp.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index d4ed9a19d8fe7..e4dc241c5a8e8 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -958,11 +958,22 @@ void tick_broadcast(const struct cpumask *mask)
}
#endif

+/*
+ * The number of CPUs online, not counting this CPU (which may not be
+ * fully online and so not counted in num_online_cpus()).
+ */
+static inline unsigned int num_other_online_cpus(void)
+{
+ unsigned int this_cpu_online = cpu_online(smp_processor_id());
+
+ return num_online_cpus() - this_cpu_online;
+}
+
void smp_send_stop(void)
{
unsigned long timeout;

- if (num_online_cpus() > 1) {
+ if (num_other_online_cpus()) {
cpumask_t mask;

cpumask_copy(&mask, cpu_online_mask);
@@ -975,10 +986,10 @@ void smp_send_stop(void)

/* Wait up to one second for other CPUs to stop */
timeout = USEC_PER_SEC;
- while (num_online_cpus() > 1 && timeout--)
+ while (num_other_online_cpus() && timeout--)
udelay(1);

- if (num_online_cpus() > 1)
+ if (num_other_online_cpus())
pr_warn("SMP: failed to stop secondary CPUs %*pbl\n",
cpumask_pr_args(cpu_online_mask));

--
2.20.1
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